The Team Sky rider jumped clear of his rival two kilometres from the summit and went on to claim stage five by 10 seconds, taking him up to fourth in the General Classifications.

Evans, who was the overnight leader, was overtaken at the top of the classifications by Orica-GreenEdge's Simon Gerrans, who now has a one-second advantage over his countryman.

Despite his slender advantage, Gerrans is now strong favourite to more than match Evans' flat speed on Sunday's final stage, a street race through the Adelaide CBD, and win a record third Tour Down Under.

Evans attempted to protect his seven-second overall overnight lead by going on the attack early on stage five, but he and his team failed to control the race in the face of a strong headwind and steep climb up Willunga Hill.

And Evans' loss was Porte gained as the Team Sky rider broke clear and conquered the climb in some style.

"That was an incredible ride," he told Sky Sports. "I think there was a lot of pent up aggression from this week that showed on that final climb. We have spoken before today that a rider with nothing to lose is always a dangerous rider. Richie rode like a rider with nothing to lose.

"He is 30 second off GC [General Classifications lead], he can't take time bonuses, so that was his only option. So he was 100 per cent committed to doing what he did today. The problem was that everyone else behind him was not committed."

Hammond criticised Evans' BMC Racing team-mates for failing to handle the conditions and control the race for their team lead. And the former two-time National Road Race Champion insisted Evans' hopes of winning the Tour Down Under are all but over now.

"I think what he is going to have to do now is defend his position on GC. We have talked about him using his team-mates, sending them up the road to take the time seconds away from third and fourth place overall but as far as taking time himself it is such a slim chance that it is something we can't really think about."